Stiff tongue syndrome and multifocal immune neuropathy in a young man with anti-glutamic acid decarboxylase and unclassified antibodies.

Anti-glutamic acid decarboxylase 65 antibody (anti-GAD65Ab)-mediated neurological syndromes are constantly expanding with recent literature descriptions of peripheral nerve involvement. This report describes a man in his 30s presenting with progressive episodic tongue stiffness and upper limb weakness, with examination revealing restricted tongue movement and asymmetric proximal predominant upper limb weakness. Electrophysiology showed conduction blocks, and imaging revealed inflammatory brachial plexus changes. Anti-GAD65Ab and an unclassified neuronal antibody were identified on serological testing. Immunotherapy led to complete resolution of tongue stiffness and recovery of limb power. Literature is emerging, associating anti-GAD65Ab with autoimmune neuropathies like Acute Inflammatory Demyelinating Polyneuropathy (AIDP) and Chronic Inflammatory Demyelinating Polyneuropathy (CIDP), even though the pathogenesis remains uncertain. This case expands the spectrum of anti-GAD65Ab-associated syndromes to include stiff tongue syndrome and multifocal immune neuropathy, highlighting the importance of recognising rare autoimmune presentations for effective immunotherapy.